Re: recovery_min_apply_delay in archive recovery causes assertion failure in latch

On Mon, Sep 30, 2019 at 12:49 AM Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>
> Hi,
>
> I got the following assertion failure when I enabled recovery_min_apply_delay
> and started archive recovery (i.e., I put only recovery.signal not
> standby.signal).
>
> TRAP: FailedAssertion("latch->owner_pid == MyProcPid", File:
> "latch.c", Line: 522)
>
> Here is the example to reproduce the issue:
>
> ----------------------------
> initdb -D data
> pg_ctl -D data start
> psql -c "alter system set recovery_min_apply_delay to '60s'"
> psql -c "alter system set archive_mode to on"
> psql -c "alter system set archive_command to 'cp %p ../arch/%f'"
> psql -c "alter system set restore_command to 'cp ../arch/%f %p'"
> mkdir arch
> pg_basebackup -D bkp -c fast
> pgbench -i
> pgbench -t 1000
> pg_ctl -D data -m i stop
> rm -rf bkp/pg_wal
> mv data/pg_wal bkp
> rm -rf data
> mv bkp data
> touch data/recovery.signal
> pg_ctl -D data -W start
> ----------------------------
>
> The latch that causes this assertion failure is recoveryWakeupLatch.
> The ownership of this latch is taken only when standby mode is
> requested. But this latch can be used when starting archive recovery
> with recovery_min_apply_delay set even though it's unowned.
> So the assertion failure happened.
>
> Attached patch fixes this issue by making archive recovery always ignore
> recovery_min_apply_delay. This change is OK because
> recovery_min_apply_delay was introduced for standby mode, I think.

No, I found the following description in the doc.

------------------------------
This parameter is intended for use with streaming replication deployments;
however, if the parameter is specified it will be honored in all cases
------------------------------

So archive recovery with recovery_min_apply_delay enabled would be
intended configuration. My patch that changes archive recovery so that
it always ignores thesetting might be in wrong direction. Maybe we should
make recovery_min_apply_delay work properly even in archive recovery.
Thought?

Regards,

--
Fujii Masao